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Clopidogrel Gets Black Box Warning for Reduced Effectiveness in Certain Patients ROCKVILLE, Md -- March 12, 2010 -- The US Food and Drug Administration (FDA) has added a Boxed Warning to the label for clopidogrel (Plavix) regarding patients who do not effectively metabolise the drug and therefore may not receive the full benefits of the drug. The Boxed Warning in the drug label will include information to: · Warn about reduced effectiveness in patients who are poor metabolisers of clopidogrel. · Inform healthcare professionals that tests are available to identify genetic differences in CYP2C19 function. · Advise healthcare professionals to consider use of other anti-platelet medications or alternative dosing strategies for clopidogrel in patients identified as poor metabolisers. In May 2009, FDA added information about poor metabolisers of clopidogrel to the drug label. However, based on additional data (see below) reviewed by the agency the Boxed Warning is now being added to highlight the reduced effectiveness of clopidogrel in these patients and to recommend that healthcare professionals consider use of other anti-platelet medications or alternative dosing strategies for clopidogrel in patients identified as poor metabolisers. Additional Data The liver enzyme CYP2C19 is primarily responsible for the formation of the active metabolite of clopidogrel. Pharmacokinetic and antiplatelet tests of the active metabolite of clopidogrel show that the drug levels and antiplatelet effects differ depending on the genotype of the CYP2C19 enzyme. The following represent the different alleles of CYP2C19 that make up a patient’s genotype: · The CYP2C19*1 allele has fully functional metabolism of clopidogrel. · The CYP2C19*2 and *3 alleles have no functional metabolism of clopidogrel. These 2 alleles account for most of the reduced function alleles in patients of Caucasian (85%) and Asian (99%) descent classified as poor metabolisers. · The CYP2C19*4, *5, *6, *7, and *8 and other alleles may be associated with absent or reduced metabolism of clopidogrel, but are less frequent than the CYP2C19*2 and *3 alleles. · A patient with 2 loss-of-function alleles (as defined above) will have poor metaboliser status. The pharmacokinetic and antiplatelet responses to clopidogrel were evaluated in a crossover trial in 40 healthy patients. Ten patients in each of the 4 CYP2C19 metaboliser groups (ultrarapid, extensive, intermediate, and poor) were randomised to 2 treatment regimens: a 300 mg loading dose followed by 75 mg per day, or a 600 mg loading dose followed by 150 mg per day, each for a total of 5 days. After a washout period, patients were crossed over to the alternate treatment. Decreased active metabolite exposure and decreased platelet aggregation were observed in the poor metabolisers compared with the other groups. When poor metabolisers received the 600 mg loading dose followed by 150 mg daily, active metabolite exposure and antiplatelet response were greater than with the 300 mg/75 mg regimen. Healthcare professionals should note that an appropriate dose regimen for patients who are poor metabolisers has not been established in clinical outcome trials. It is estimated that 2% to 14% of the population are poor metabolisers; the rate varies based on racial background. SOURCE: US Food and Drug Administration E-mail this page to a friend or colleague! To print, use this version